The present invention relates generally to a detector arrangement and more specifically to a detector arrangement which is designed to detect in a stream of loose material the presence of one or more individual particles that has/have a temperature and/or an energy content such as to be able to incite fire or cause an explosion to take place in a downstream particle or material collecting risk zone.
By loose material is meant any type of material that can be transported by or in a gas mixture, normally air, wherewith the individual particles of the loose material are normally spaced from one another.
Loose material of this kind may consist of very fine particles in the nature of dust, or may consist of powder particles or granular particles. Wood chips, pellets, straw and like materials can also be transported in this way.
The inventive detector arrangement is adapted to be included in a preventative, protective system that includes one or more sensor units, an evaluation unit evaluating the output signals of said sensor units, and an activation unit connected to said evaluation unit, wherein at least one individual particle that can be sensed by the sensor units and having an energy content determined in the evaluation unit as exceeding a predetermined value will cause the activation unit to switch from a first state (a rest state) to a second state (an activating state).
More particularly, the detector arrangement can be adapted for use in a process in which loose, process material is produced in a first unit and transported therefrom to a receiving, second unit, wherein treatment of said material in said first unit may result in one or more particles being heated to a temperature that is sufficiently high to initiate fire and/or an explosion in at least the second unit, and in which arrangement the transport system required to transport the loose material between said first unit and said second unit includes a stabilising zone or disturbance zone, a zone that indicates the presence of high temperature particles, an effectuating zone, an extinguishing zone, and a downstream risk zone adjacent to or within said second unit.
The stabilisation zone is intended to allow particles that have a low energy content and do not constitute a fire risk or explosion risk within the downstream located zones, and particularly within the risk zone, to reduce their energy content and therewith prevent said particles being indicated as a hazard within the immediate downstream indication zone.
The indication zone includes one or more sensor units which function to indicate the presence of one or more individual particles whose energy content is liable to incite fire or some other damage should said particle or particles appear in the downstream zones and then particularly in the risk zone.
Each of the aforesaid sensor units can co-act with a unit which evaluates the output signals of a sensor unit, and with an activation unit such that when the sensor units indicate the presence of such a hazardous particle, the activation unit will activate an extinguishing means associated with said extinguishing zone and/or a particle removal means.
The indication zone is followed by an effectuating zone whose length is adapted so that upon activation of means in said extinguishing zone said means will have time to generate an extinguishing barrier before or as the particle reaches said zone.
The extinguishing zone may also include a valve, which deflects a collection of material containing said particle from the transportation path to the risk zone.
A preventative, protective system that includes one or more sensor units and associated detector arrangements of the aforedescribed kind is previously known and marketed by Firefly AB, Stockholm, Sweden. The preventative, protective system functions to indicate sparks and individual, glowing particles in a stream of loose material, such as granular material or dust, and to apply extinguishing means or smothering means so as to prevent such glowing particles from reaching the downstream process unit, such as a filter, a silo or the like, or from reaching the risk zone, which would otherwise be set on fire and/or caused to explode.
The preventative, protective system utilises in operation various detector systems and detector arrangements for sensing and detecting individual particles.
With regard to sensor units included in detector arrangements of the aforesaid kind and similar preventative applications, it has been found that they have a delayed reaction in industrial processes or are not sufficiently sensitive to be considered as an effective damage limiting means, which also applies to the output signal evaluating unit and the activation unit.
Sensor units of this kind tend to react to individual particles that are not harmful in certain circumstances, while in other circumstances they fail to react to individual particles that can cause damage by fire or explosion.
In this regard, it has been found necessary to maintain a safety range that is so large as to cause the equipment to react to particles that can cause no damage rather than not react to particles that are liable to cause damage, this being a preferred safety measure.
It is known to use temperature detectors in the present context, although experiences have shown in practice that these detectors often fail to react until a fire has already developed.
Although flame detectors used in the present context are sensitive to small (low) flames, their use in a preventative, protective system is excluded because they react much too late.
It is also known to use pressure detectors that operate with high sensitivity and with small time constants, but also such detectors normally require an initial explosion or combustion in order to react.
It is also known to use wavelength-related detector arrangements.
Practical experiences, however, indicate that even discrete particles that radiate solely within one wavelength range, solely for thermal radiation in a transport path, having a temperature in the range of 400xc2x0 C. are a fire and explosion risk in various process plants where combustible, finely divided and loose material is transported with the aid of a vehicle gas or vehicle gas mixture, preferably an air stream.
The contents of Patent Publication U.S. Pat. No. 5,193,622, which describes a detector arrangement that includes a sensor unit, also belongs to the known prior art. Patent Publication SU-A1-1,729,528 teaches a detector arrangement that includes several sensor units.
With respect to the features associated with the present invention, it can be mentioned that Patent Publication U.S. Pat. No. 5,749,420 describes a detector arrangement in which an indicating and activating unit 12 is adapted to evaluate and sense the radiation intensity from each of a number of sensor units 105, 107.
With respect to the aforementioned publications, the sensor units used are adapted to receive summated each wavelength-related radiation intensity from a large wavelength range or from the whole of the wavelength spectrum of the particle.
When taking into consideration the technical deliberations that a person skilled in this particular art must make in order to provide a solution to one or more technical problems that he/she encounters, it will be seen that on the one hand it is necessary initially to realise the measures and/or the sequence of measures that must be undertaken to this end, and on the other hand to realise which means is/are required to solve one or more of these problems, and on this basis, it will be evident that the technical problems listed below are highly relevant to the development of the present invention.
With respect to the singularities associated with the present invention, it is necessary to realise that each individual, discrete particle of loose particulate material carried in a transport system that has an elevated energy content will generate radiation that can spread within a wide wavelength spectrum which may extend from the range of ultraviolet radiation (UV radiation) to the infrared radiation or thermal radiation range (IR radiation) via visible radiation, and that thermal radiation is of particular significance to the system in the case of many applications.
This wavelength spectrum or large wavelength range can also be divided into a number of narrow wavelength ranges.
When considering the present state of the art as described above, it will be evident that a technical problem resides in creating with the aid of simple means a detector arrangement that is highly reliable and with which the activation unit will take an activation mode solely when there is a real danger of fire or a corresponding hazard, and which enables the safety range to be kept within narrow limits.
It will also be seen that a technical problem is one of realising the significance of establishing, usually empirically, an adapted, relevant large wavelength range within which the wavelength spectra of the particles can be evaluated, with respect to every process plant and combustible, finely divided loose material used therein.
Another technical problem is one of realising the significance of establishing for each process plant and the combustible, loose, finely divided material used therein, a suitable number of narrow wavelength ranges and the width of the wavelength ranges located within the adapted large wavelength range that is the subject of evaluation, said number of narrow wavelength ranges normally being established empirically.
It will also be seen that a technical problem is one of realising the significance of adapting the width of each of the selected number of wavelength ranges in dependence on the process plant used and the loose material handled therein, so as to provide a high safety factor within a narrow safety range, and so that activation of relevant safety means will only take place in the event of real danger.
It will also be seen that a particularly technical problem is one of enabling the total energy content of a single particle to be evaluated with the aid of simple means, by evaluating and signal-processing only relevant intensity values that can be evaluated within chosen, limited narrow wavelength ranges.
Another technical problem resides in the ability to approximate a complete intensity curve for-a single particle with the aid of a few measuring points, by choosing measuring points within a limited, relevant wavelength range.
Another technical problem is one of realising the significance of and the advantages associated with establishing, normally empirically, for each process plant and loose combustible material handled therein an adapted sub-intensity value for each evaluatable narrow wavelength range, so that the activation unit will be able to adopt an activation state immediately when only one or a few of the sub-intensity values sensed exceeds/exceed a corresponding, adapted and determined sub-intensity value.
Another technical problem resides in choosing from among a total number of available wavelength ranges a smaller number of narrow wavelength ranges which must indicate in respect of a single particle the sub-intensity values that correspond to or exceed established and adapted sub-intensity values so as to cause the activation unit to adopt an activation mode, this choice being made in respect of each process plant and the combustible material handled therein.
With regard to the known prior art as described above, the primary aim of the present invention is to provide an improved detector arrangement which is able to evaluate the energy content of loose, discrete particles in the process plant in a more positive and more simple manner, and also to be able to detect and indicate single particles that have a temperature slightly below 400xc2x0 C.
Another technical problem is one of realising the advantages that are afforded when at least two of the sensor units or sensor sections in the inventive detector arrangement have sensing lobes which cover the cross-section of a loose material transportation path, and to accurately establish the energy content of an indicated single particle on the basis of received signals related to a narrow wavelength range, regardless of the orientation of the particle in said cross-section and while taking the distance from respective detectors into account.
In this respect, a technical problem resides in creating with the aid of simple means a detector arrangement in which a first sensor unit or section of said unit is able to sense, or detect, the sub-energy content of a single particle present and the sub-intensity value within a first narrow wavelength range, and that a second sensor unit or section thereof is adapted to sense, or detect, the sub-energy content and sub-intensity value of said particle within a second narrow wavelength range, and that an evaluating unit is adapted to process the output signals from both said sensor units and accordingly either inhibit actuation of an activation unit to an activation mode or to cause said activation unit to switch to its activation mode.
Another technical problem is one of realising the significance of and the advantages that are afforded by adapting a sensor unit to sense, or detect, the sub-energy content of a particle within mutually separate, narrow wavelength ranges located within the full wavelength spectrum of the particle radiation with respective wavelength ranges having one and the same width or mutually different widths.
Another technical problem is one of realising the significance of and the advantages that are afforded when a plurality of sensor units or sensor sections are adapted to sense, or detect, the sub-energy content of a particle and/or its sub-intensity within mutually overlapping wavelength ranges.
Another technical problem is one of realising the significance of and the advantages that are afforded by allowing the evaluating unit to compare the sub-intensity of a received output signal with a stored and maximised wavelength range value, and to actuate the activation unit in the event of the sub-intensity of an output signal exceeding said maximised value.
Another technical problem is one of realising the significance of and the advantages that are afforded by enabling the evaluating unit to compare the sub-intensities of a plurality of received output signals with a plurality of stored, maximised wavelength range values and to cause the activation unit to switch to its activation mode when the sub-intensities of predetermined output signals and/or with a predetermined number of output signals exceed said maximised value.
Another technical problem is one of realising the significance of and the advantages that are afforded by choosing said narrow wavelength ranges with a wavelength within the heat radiating range, such as a wavelength greater than 1.0 xcexcM.
Another technical problem is one of realising the significance of and the advantages afforded by choosing a narrow wavelength range or narrow wavelength ranges that have a wavelength within 1.2 to 5.0 xcexcM, such as 1.4 to 3.5 xcexcM.
Another technical problem is one of realising the significance of and the advantages afforded by adapting the chosen narrow wavelength ranges and the maximised wavelength values related thereto in accordance with one or more of the following criteria: choice of material to be transported, material in anticipated particle presence, the design of the preventative, protective system, the process concerned, etc.
Another technical problem is one of realising the significance of and the advantages afforded by adapting a sensor unit or sensor sections to evaluate the sub-energy content of a particle within at least three, preferably more, and, e.g., up to ten, different narrow wavelength ranges located within the full wavelength spectrum of the radiation.
It will also be seen that a technical problem is one of realising the significance of and the advantages afforded by adapting the evaluating unit to evaluate a sensed, or detected, sub-intensity-dependent wavelength-related output signal deriving from a narrow wavelength range from each of said sensor units or sensor sections, and to co-ordinate the sub-intensity-dependent signals so as to be able to calculate and also to establish the relevant energy content of the particle and its disposition to initiate fire and/or explosion in a downstream risk zone.
It will also be seen that a technical problem is one of realising the significance of arranging said sensor units or sensor sections, each being allocated a narrow wavelength range, diametrically and/or uniformly around an inner peripheral surface of a tubular conduit of circular cross-section, and then to realise the significance of the orientation of the number of sensor units and/or sensor sections used.
It will also be seen that a technical problem resides in realising the significance of positioning the sensor units and/or the sensor sections opposite one another about an inner perimeter surface of a tubular conduit of angular cross-section and to realise the significance of placing the sensor units and/or the sensor sections in the corners of said conduit.
Another technical problem is one of realising the significance of coordinating the sensor units symmetrically and diametrically opposite one another around an inner peripheral surface of a tubular conduit having a right-angled cross-section, and to realise for which applications said sensor units and/or said sensor sections shall be placed in the corners of said conduit.
Another problem resides in realising the advantage of using a sensor unit and/or a sensor section that has a detection angle of about 180 degrees and a sensing lobe that has a corresponding semi-circular shape.
Another technical problem is one of realising the significance of covering each sensor unit and/or its sensor section with a protective cover that includes a plurality of mutually adjacent slots, said slots preferably being orientated in a direction perpendicular to or generally perpendicular to the feed direction of said material, and all of the sensor units and/or the sensor sections being co-ordinated around one and the same cross-section plane through the transport paths.
Another technical problem is one of designing the sensor unit in accordance with circumstances that prevail at a particular time, either by adapting a sensor unit to evaluate the sub-intensity values for a plurality, such as all, chosen narrow wavelength ranges, or by choosing a number of sensor units which are each adapted to evaluate the sub-intensity value of one narrow wavelength range or of a few narrow wavelength ranges.
With the intention of solving one or more of the aforesaid technical problems, there is provided in accordance with the present invention an arrangement which can be included beneficially in a preventative, protective system of the aforedescribed kind, said arrangement including light-sensitive and heat-sensitive devices in the form of a sensor unit and associated sensing circuits for detecting a single particle that has a high energy content.
There is normally used in such a detector arrangement at least two sensor units or sensor sections whose sensing lobes are intended to cover a cross-section of the transportation path of loose particulate material.
The present invention relates particularly to a detector arrangement which can be adapted for inclusion in a preventative, protective system and that includes a number of sensor units or sensor sections, a unit for evaluating the output signals of said sensor units and an activation unit which is coupled to the evaluating unit, wherein sensing of at least one individual particle whose energy content established in the evaluating unit is found to exceed a predetermined value is able to switch the activation unit from a first state to a second state.
It is particularly proposed in accordance with the present invention that a first sensor unit or sensor section is adapted to sense the sub-energy content of said individual particle and/or its sub-intensity value within a first narrow wavelength range, that a second sensor unit or sensor section is adapted to sense the sub-energy content of the same individual particle and/or its sub-intensity value within a second narrow wavelength range, and that an evaluating unit is adapted to allow the output signals from both sensor units or sensor sections to be processed and to inhibit actuation of the activating unit to its activating position or to cause said activation unit to switch to its activation state on the basis of the result.
By way of preferred embodiments that lie within the scope of the present invention, it is proposed that a plurality of sensor units or sensor sections are adapted to sense the sub-energy content of a particle and/or its sub-intensity value within a number of mutually separate narrow wavelength ranges.
A plurality of sensor units or sensor sections may be adapted to sense the sub-energy content of a particle within mutually overlapping wavelength ranges.
It is also proposed that the evaluating unit shall be adapted to allow a comparison to be made between the sub-intensity of a received output signal and a stored maximised wavelength range-related value and to cause the activation unit to switch to its activating mode when the sub-intensity of an output signal exceeds said maximised value.
The evaluating unit will preferably be adapted to compare the intensity of a plurality of received output signals with a plurality of stored maximised values related to wavelength ranges and to cause the activation unit to switch to its activating mode only when the sub-intensities of a predetermined number of output signals exceed said maximised values.
Each of the narrow wavelength ranges will preferably have a wavelength greater than 1.0 xcexcM.
More specifically, said narrow wavelength ranges are chosen from within a selected large wavelength range, such as 1.2 to 5.0 xcexcM.
The selected narrow wavelength ranges and the maximised values related thereto are adapted to one or more of the following criteria: the nature of the material being transported, the nature of the material in said particle, the design of the preventative, protective system, the process concerned, etc.
It is also proposed that a sensor unit or a number of sensor sections are adapted to evaluate the energy content of an individual particle present and/or its intensity within at least three narrow wavelength ranges located within the total wavelength spectrum or a chosen large wavelength range with respect to the radiation emitted by an individual particle.
It is also proposed in accordance with the invention that the evaluating unit and the activation unit are adapted to evaluate a sensed wavelength-related sub-intensity from each of said sensor units or sensor sections, and to co-ordinate the received sub-intensity-dependent wavelength-related signals so as to be able to calculate and establish therefrom the energy content or the like of said particle and therewith be able to estimate the disposition of the particle to initiate relevant fire and/or explosion criteria in respect of a specific system and its material properties.
By way of proposed embodiments that lie within the scope of the inventive concept, it is proposed that said sensor units or sensor sections are disposed diametrically opposite one another or are uniformly spaced around the inner perimeter surface of a tubular conduit of circular cross-section.
It is also proposed that said sensor units or sensor sections are disposed opposite one another around the inner perimeter surface of a tubular conduit of angled cross-section, and to place said sensor units or sensor sections in the corners of said conduit.
The sensor units or sensor sections are disposed symmetrically and in mutually opposed relationship around the inner perimeter surface of a tubular conduit of right-angled cross-section, and are preferably placed in the corners of said cross-section in respect of certain applications.
According to the invention, each sensor unit or sensor section has a detection angle of about 180 degrees.
It is particularly proposed that each sensor unit or sensor section can be covered with a protective cover that includes a plurality of mutually adjacent slots that are orientated in a direction perpendicular to or substantially perpendicular to the feed direction of said material, and that all sensor units or sensor sections are orientated in one and the same plane or are at least orientated so that an individual particle passing two or more sensor units or sensor sections can be evaluated simultaneously or generally simultaneously by all of said sensor units or sensor sections.
The invention also enables the use of one single sensor unit that is constructed to evaluate all of the intensity values relating to the chosen narrow wavelength ranges, or a chosen number of sensor units which are each adapted for evaluating the sub-intensity value of a narrow wavelength range or of a few narrow wavelength ranges.
Those advantages that are primarily afforded by an inventive detector arrangement and particularly when said arrangement is included in a preventative and protective system reside in the provision of conditions which enable two or more sensor units or sensor sections to evaluate the high energy content of individual, loose particles passing said sensor units or sensor sections with greater precision than was earlier possible regardless of the position of the particle within a cross-section of its path as a result of sensing such a particle in each of the sensor units or sensor sections simultaneously with mutually discrete and narrow wavelength ranges located within the wavelength spectrum of the total radiation of the particle and by processing the sub-intensity signals generated by said single particle from each of the sensor units or sensor sections so as to enable the relevant energy content of the particle to be established and to cause an activation unit to be brought to an activating mode when said energy content exceeds a predetermined value.
In particular, a plurality of sensor units or sensor sections evaluate sub-intensities of the particle and on the basis of these sub-intensities and a stored control value the relevant energy content of the particle is evaluated and an activation circuit is activated when this evaluated value exceeds a predetermined value.
The main characteristic features of an inventive detector arrangement are set forth in the characterising clause of the accompanying claim 1.